1. Field of the Invention
My invention relates to capacitors, and more specifically to a tubular type of capacitor having at least two electrodes formed on a tube of ceramic or like dielectric material and held in mechanical and electrical contact with a pair of metal caps pressed onto the opposite ends of the dielectric tube.
2. Description of the Prior Art
Tubular ceramic capacitors of the type in question have had a problem concerning the desired mechanical and electrical contact between electrodes and metal caps. The dielectric tube forming the insulation between the electrodes of the capacitor is usually fabricated by extruding into tubular form a mixture of a ceramic material composed principally of barium titanate (BaTiO.sub.3), strontium titanate (SiTiO.sub.3) or the like, and a binder. The tubular extrusion is cut into desired lengths, and these are then sintered or heated into coherent bonded bodies for use in capacitors.
The above sintering operation causes contraction of the ceramic tubes to varying degrees, up to approximately 20% of the original size. In view of such inevitable dimensional errors of the ceramic tubes, a pair of metal caps pressed onto the opposite ends of each ceramic tube, following the formation of electrodes thereon, have usually been each slitted to provide a plurality of spring fingers, as disclosed for example in J. E. Toppari et al. U.S. Pat. No. 3,233,028. The use of such slitted metal caps, however, is insufficient to ensure their firm mechanical and electrical contact with the electrodes on the ceramic tube. J. E. Toppari et al. further suggest a plastic insulating case molded around and completely enclosing the capacitor. This measure is still unsatisfactory, however.
Another important problem concerning tubular ceramic capacitors is the maintenance of their desired electrical properties for as long a period of time as possible. This objective can be attained in part by isolating the interior of the ceramic tube from the atmosphere. J. E. Toppari et al. teach to fill the bore of the dielectric tube with a thixotropic gelable silicone dielectric liquid, which is gelled in situ.
It may be contemplated, as an alternative, to form joints of solder or conductive paint between metal caps and electrodes on the ceramic tube, for the accomplishment of the dual objective of mechanically and electrically connecting the metal caps and electrodes and hermetically sealing the interior of the ceramic tube. This measure is objectionable because the solder or conductive paint is likely to flow into the interior of the capacitor thereby short-circuiting the electrodes. As an additional disadvantage, the joints of solder or conductive paint are incapable of withstanding all operating temperatures.